Due to the increasing energy demands, offshore oil and gas production is moving into deeper waters. For ensuring an efficient and secure production, processing facilities are being installed at the ocean floor. Such subsea installations can comprise a range of components, including pumps, compressors and the like. A subsea power grid can be provided for operating these components. The power grid may for example comprise a subsea transformer, subsea switchgear and subsea variable speed drives. The components of the subsea installation need to be protected from the surrounding sea water, in which pressures of 300 bars or more can prevail (at installation depths of 3.000 m or more).
To protect subsea equipment from overcurrents or short-circuits, fuses can be installed which interrupt an electrical connection if the current through the fuse becomes too large. A conventional fuse comprises a fuse body and a fuse element. The fuse element is generally a metal strip or wire and is connected between two electrical terminals of the fuse. At currents above the rated current, the fuse element melts, thereby interrupting the electrical circuit. The faulty circuit can thus be isolated, whereby damage to other electric components of the system can be prevented.
For providing a fuse for subsea applications, a conventional fuse can be placed into a pressure resistant canister which is maintained at a pressure of about one atmosphere. The canister needs to be thick walled in order to withstand the high pressures at water depths of up to 3000 m or even more. Sophisticated penetrators capable of bridging such high pressure differences are further required to provide an electrical connection to the fuse through the walls of the canister. This solution of providing a fuse for a subsea application is very cost intensive due to the canister and the penetrators and further requires a considerable amount of space. The canister is also very heavy.
More recently, solutions were proposed in which electric components are placed in pressure compensated canisters. The canisters are filled with a dielectric liquid and a pressure is maintained inside the canister that is almost equal to the surrounding water pressure. Standard fuses are generally incompatible with such environment. The inventors have found that the dielectric liquid changes the properties of a conventional fuse significantly. The fuse will still be capable of breaking a current when triggered, but this will cause an explosion inside the fuse, which can be detrimental to other electric components (e.g. due to a shockwave or shrapnel). Further, the combustion products of the explosion can contaminate the surrounding dielectric liquid severely. This can cause failures in other components exposed to the dielectric liquid. Conventional fuses can thus not be used in a pressurized environment.
A solution to this problem is proposed in the document EP 2495746 A1, which describes a subsea fuse assembly.